The present invention relates to a non-invasive patient immobilisation assembly for immobilising a body part of a patient and for at least temporarily fixing the position thereof, wherein the immobilisation assembly comprises a rigid template made of a thermoplastic material, which template is thermoformed or otherwise moulded in such a way that the inner surface conforms to and contacts the body part to be immobilised along a contact surface area which corresponds to at least part of the inner surface of the template, wherein the immobilisation assembly also comprises a fixation plate and connecting means for connecting the template to the fixation plate in view of fixing the position of the template and the body part with respect to the fixation plate, as described in the preamble of the first claim.
Devices immobilising the position of a patients' head or other body part are used to allow for an accurate and reproducible positioning and re-positioning of the body part involved in medical diagnostic imaging and in treatment procedures, as for example in radiation therapy and in surgery. Fractionated treatment (for example MIRT) involves the division of a radiation dose into a multiplicity of sub doses delivered to a patient on different points in time to allow for a maximum recovery of healthy tissue and to minimise complications from overexposure to radiation. In particular when exposing a patients' head to fractionated treatment, precise positioning and highly accurate, reproducible re-positioning of the target and surrounding normal structures of the head is a pre-requisite to ensure that the radiation is delivered exactly at the target position where it is needed, for example a tumor, while minimising the risk to exposure of surrounding healthy tissue.
U.S. Pat. No. 3,957,262 discloses a device for immobilising a patient's head during surgery or examination. The device comprises a headpiece in the form of a cap for receiving and supporting the back of the patient's head that is not to be examined. The interior of the headpiece is made of soft rubber foam which conforms to the size and shape of the back of the patient's head to be supported by it. The patient's head is restrained in a certain position within the cap by means of a chin restrainer and forehead restrainer. The restrainers take the shape of a band, both ends of which are fastened to opposite sides of the hole containing the head. The bands extend over a part of the face, provide a local fixation only and still permit moving of eyes, nose, lips, cheeks etc, thus the parts that have to be subjected to treatment. Because of the limited size, a high local tension will be sensed by the patient's face at the position of the bands. The device further comprises means for changing the distance between the headpiece and the surface supporting the headpiece and the patient. However, there is no indication in U.S. Pat. No. 3,957,262 that the material, of which the cap, chin and forehead restrainer are made, is transparent to irradiation. U.S. Pat. No. 3,957,262 does not recognise the need to an accurate re-positioning of the head which is to be subjected to treatment. U.S. Pat. No. 3,957,262 does not recognise the problem that the dimensions of the head may vary in the course of the fractionated treatment, and does not provide the means to adapt the shape and dimensions of the cap accordingly. This is particularly important with fractionated treatment and irradiation of the head or face, which should be carried out with the best obtainable reproducibility.
DE-U-279.11833 teaches to configure the position of a patient with respect to a supporting surface, by means of a radiation transparent shield covering the patient. A plurality of inflatable cushions are mounted to the inside of the shield. In the inflated state, the cushions configure the position of a patient. However, DE-U-279.11833 does provide the means which permit a reproducible positioning of the patient over longer periods of time associated with fractionated treatment, where days, weeks or more may lapse between subsequent treatments. The reason is that the cushions are re-inflated before every treatment. If the body takes a slightly different position as compared to a previous treatment, this will be taken over by the cushions upon inflation.
U.S. Pat. No. 5,370,117 discloses a patient immobilisation system for repeated use in imaging and treatment of brain tumors, comprising an immobilisation plate onto which a positioning mask is to be fixed. On opposite sides of the immobilization plate a pair of side rails are mounted, studs protruding from the outer face of the side rails. The mask is formed over the head of the patient, holes provided along the side edges of the mask are slipped over the studs. The mask is held in place against the side rails by means of a pair of anchor bars having a multiplicity of holes adapted to engage the studs. Thus, the lower ends of the mask are received between the outer face of the side rails and the anchor bars. To prevent the mask from wobbling from side to side, the lower ends of two vertical leg portions of a relatively rigid arc are secured to the outer edge of the anchor bars, the apex of the arc being connected to an upwardly disposed flap of the mask. Between the pair of side rails, a head and neck support may be slideably mounted. This immobilisation system is however only concerned with improving the accuracy of the mask positioning with respect to the immobilisation plate, but does not address the problem of restraining the movability of the patient's head within the contours of the mask, nor is it concerned with the reproducibility of the patient positioning in fractionated treatment.
US2002/108616 discloses an invasive patient immobilisation system, comprising a mouth piece fixation member to be received within the patient's mouth, and a thermoplastic mask which is formed to the patient's face by placing the softened thermoplastic material across the patient's face, in such a way that it also extends over the mouth piece fixation member. While the thermoplastic mask is left to cool and harden, a fastener plate is coupled to the mouth piece fixation member to fix it to the thermoplastic mask. Following cooling, the mask reflects the contours of the patients face. However, the presence of the additional member in the mouth is uncomfortable to the patient and adds an additional member which may hamper irradiation. Similar to the above discussed prior art publications, US2002/108616 does not address the problem of restraining the movability of the patient's head within the contours of the mask, nor is it concerned with the reproducibility of the patient positioning in fractionated treatment.
U.S. Pat. No. 5,566,681 discloses a non-invasive device for stabilising or immobilising a specific body part to a support frame. The device comprises a rigid thermoplastic template, which provides a personal fit for the support and stabilisation of the body part to be immobilised. The template is obtained by softening the thermoplastic sheet, forming it to the body part to be immobilised, and cooling it to confine it into the moulded shape. The rigid template may include a plurality of fiducial markers affixed to it, to provide reference points for guidance during surgery. Thus the need can be overcome to apply fiducial markers to the body part or to a positioning apparatus. However, once moulded to the body part, the thermoplastic template cannot take account of any changes that have been occurred with the size or shape of body part that needs immobilisation. Shrinking of the body part following weight loss, will result in a fitting of the template which is insufficiently tight and allows the patient to move within the template; growing of the body part to be immobilised will result in a too tight, uncomfortable fit. Remoulding is not an option as the position of the fiducial markers after remoulding will not conform to the original position.
There is thus a need to an immobilisation device which goes beyond envisaging a precise positioning of the body part with respect to a diagnostic or treatment device for one single time. In particular there is a need to an immobilisation device which allows for a precise and reproducible re-positioning of each part of a body part with high accuracy, even in case of fractionated treatment where time intervals of varying duration may elapse between subsequent treatments, which provides the desired comfort to the patient and does not exert excessive local pressure, and which allows to take account of varying dimensions of the body part involved in the course of a fractionated treatment while maintaining the required standards of the accuracy and reproducibility required when re-positioning the body part with respect to the treatment device. A precise positioning of the target position and surrounding normal structures of the body part with respect to the diagnostic/treatment irradiation devices is essential to ensure that exposure is limited to the envisaged tissue and the risk to damaging surrounding healthy tissue is minimised.
It is therefore the object of the present invention to provide a non-invasive immobilisation device with which a precise and reproducible positioning and re-positioning of the patients' body part to be treated may be achieved in the course of fractionated treatment or examinations, even when occurring after time intervals of varying lengths and with varying dimensions of the body part over the treatment period and which at the same time provides improved comfort to the patient.
It is a particular object of this invention to provide a non-invasive immobilisation device with which a precise re-positioning of the patients' head can be achieved, with varying dimensions of the head, without this going at the expense of comfort to the patient.